Faster Change Means Bigger Problems

From: Center for International Climate and Environmental Research

OSLO, NORWAY — The debate about what constitutes "dangerous anthropogenic interference with the climate" has almost exclusively focused on how much the temperature can be allowed to increase. But we have perhaps just as much reason to be concerned about how quickly these changes take place.

The UN Framework Convention on Climate Change (UNFCCC) aims to avoid what is called "dangerous anthropogenic interference with the climate system".

However, there is no guarantee that the level of climate change - how much the temperature increases in the future - is the only thing we should be worried about. How quickly the changes take place can also mean a lot for how serious the consequences will be. This was already acknowledged when the UNFCCC was signed in 1992. It says that we must stabilize the concentrations of greenhouse gases in the atmosphere within a time period that allows ecosystems to adapt and economic development to continue, and that ensures that food production will not be threatened. This focus on rate of change has, however, not been reflected to any noticeable degree among either scientists or politicians.

There are a few studies that focus on the consequences of the rate of climate change. Most of these are ecological studies. They leave no doubt that the expected rate of change during this century will exceed the ability of many animals and plants to migrate or adapt. Leemans and Eickhout (2004) found that adaptive capacity decreases rapidly with an increasing rate of climate change. Their study finds that five percent of all ecosystems cannot adapt more quickly than 0.1 °C per decade over time. Forests will be among the ecosystems to experience problems first because their ability to migrate to stay within the climate zone they are adapted to is limited. If the rate is 0.3 °C per decade, 15 percent of ecosystems will not be able to adapt. If the rate should exceed 0.4 °C per decade, all ecosystems will be quickly destroyed, opportunistic species will dominate, and the breakdown of biological material will lead to even greater emissions of CO2. This will in turn increase the rate of warming.

According to the Intergovernmental Panel on Climate Change (IPCC), the global average temperature today is increasing by 0.2 °C per decade.

There is also a risk that rapid climate change will increase the likelihood of large and irreversible changes, such as a weakening of the Gulf Stream and melting of the Greenland ice sheets. Rapid change also increases the risk of triggering positive feedback mechanisms that will increase the rate and level of temperature change still more.

We know far less about the consequences of rate of temperature increase than we do about the level. Nevertheless, we know enough to say that if we are to avoid dangerous climate change, then we should also be concerned about how quickly it occurs. This can have important implications for which climate measures we should implement. If we set a long-term climate goal - such as 2 °C - there will be many different emissions paths we could take to reach this goal. But these emissions paths can differ to a relatively large degree with respect to how quickly the changes will take place - especially over the next few decades.

Focusing on the rate of climate change can imply that we should concentrate more on the short-lived greenhouse gases - such as methane and tropospheric ozone - and particles with a warming effect, such as soot (black carbon). It can also imply a greater focus on the medium-term (the next few decades), since the fastest changes could occur around that time.